1. Field of the Invention
The invention relates to a polarized electromagnet comprising:
on the one hand, a first magnetizable structure formed by a core placed longitudinally in the axis of symmetry of a coil adapted for receiving a DC current and by two widened pole portions integral with the core which extend transversely outside the coil;
on the other hand a second permanent magnetic structure formed by a second longitudinal magnetizable piece which has two transverse extensions directed towards the axis and which is parallel to a third magnetizable piece closer to the axis and to which it is connected by a permanent magnet with transverse magnetic axis;
opposite ends of this third piece and regions of these extensions adjacent thereto being separated by two air gaps placed substantially along a longitudinal direction so that attraction, respectively repulsion forces of the same longitudinal direction are developed between each of the respective widened pole portions placed in each of the air gaps and the second structure.
2. Description of the Prior Art
Such polarized electromagnets which are in particular applicable to controlling switching apparatus such as relays or contactors and which are known from the patent FR No. 2 358 006 may of course have a symmetrical construction about the single natural axis of symmetry formed by the axis of the coil.
It is clear that the symmetrical development of such a structure causes well known effects to appear; thus, with such a construction, the attraction forces may certainly be doubled by placing their resultant on the common axis of symmetry and the whole of the pieces which form the magnetic circuit may be made heavier without for all that changing the nature of the first results obtained, namely: a relative rectilinear movement of the first and second structures parallel to the axis complete closing of the flux of the magnet in each of the two opposite stable positions and reduction of the magnetic interferences obtained by orientating the axis of the magnet perpendicularly with respect to that of the coil.
In such an electromagnet, the repulsion and attraction forces which appear between the widened pole portions and the extensions on the one hand and between the widened pole portions and the ends on the other, communicate to the two structures forces in opposite directions, the use of the useful direction of which is in fact a simple matter of choice; each of the two possible choices give only clearly foreseeable results whose contents may at any time be used depending on the needs. Obtaining these foreseeable results in no wise modifies moreover the presence and use of the first results which are mentioned above.
French patent No. 1 603 300 which relates to a polarized electromagnet in which the magnetizable piece is mobile through the coil further mentions a possible use of such symmetrical arrangements which does not cause for all that a change to appear in the nature of the physical phenomena governing the operation.
In connection with the foregoing discussion, there may also be mentioned the additional faculty which a user may take advantage of by simultaneously giving to the first and second structures particular freedoms of movement whose relative amplitude is put to use by a common mechanism, such as the principle thereof is illustrated for example in patent DE No. 1097 563.
The measures which on the other hand may be taken for adapting the known behavior of an electromagnet to a particular class of apparatus or functions must however be more carefully examined to the extent that certain prescriptions or precautions specific to these apparatus respectively to these functions sometimes force the user either to adapt the physical behavior of the electromagnet so as to obtain well defined results or else to choose, in an overall region of operation, a region particularly well adapted to obtaining such results.
Thus, a great interest, which is justified by the constant search for safety and by that of more and more reduced consumption is attached to the automatic return to the rest position of a relay or contactor independently of the state of wear of its contacts and its movement towards the working position with reduced coil ampere turns; the gradual reduction of the dimensions of such contacts, which has an influence on the overall forces to which the mobile armature is subjected at the time of de-energization of the coil, may in fact cause one to fear the effects of remanent attraction which is frequently observed in polarized electromagnets.
The same fear of seeing the intensity of the resilient recall forces of the armature reduced and so of leaving an unfavorable overall attracticn force in existence in the rest state, may result from the efficiency reducing character which may be introduced by a transmission lever when, with a small stroke of the mobile armature, it becomes necessary to place a movement step-up lever between the armature and the mobile contacts of a switching apparatus whose own stroke must be greater than the preceding one.
The invention provides therefore a polarized electromagnet having a symmetrical lay out which uses elements corresponding to the above mentioned construction, improvements designed to reduce the power required by the coil for ensuring its change of state when this electromagnet is at rest and to allow this electromagnet to be adjusted so that the mobile assembly starts to move on the rising voltage.